Sesamum indicum L is a domesticated crop and the most ancient oil seed known from Vedic times. It is grown primarily in the tropical and a subtropical region of the world. The world production of Sesame seed is approximately 3 million metric tones (MMT) and the Sesame oil availability is about 0.75 MMT. The major producers and processors of Sesame seed are India and China (25% each), Myanmar (10-13%), Sudan (10-12%), Japan (approximately 3%) etc. Though Japan is not a producer, it is a major importer (25%) and consumer, followed by European countries, USA and Canada. India and China are known for production, use and export of Sesame seed and its products. Traditional method of Sesame oil extraction in India was by ghani but commercial extraction now employs expeller, rotary, hydraulic press and solvent extraction of oil cake. Of the total production of Sesame oil (0.2 MMT), about 75% is used for edible. purpose, 5% for Vanaspathy industry and about 4% for industrial use as paints, soaps, perfumes etc. It has been known for many years that Sesame oil is highly resistant to oxidative deterioration as compared to other edible oils. This is attributed to the presence of biologically active compounds namely lignans and lignan glucosides. Lignans are a group of natural products of phenylpropanoid origin. The main lignans in Sesame oil are Sesamin and Sesamolin. Several food, industrial and pharmaceutical uses have been reported for these lignans. Studies have shown that Sesamin, the major compound present in Sesame inhibits cholesterol absorption and synthesis in rats. Both Sesamin and Sesamolin were reported to increase hepatic mitochondrial and peroxisomal fatty acid oxidation rate [J. B. Moriss In: Food, Industrial, Nutraceutical and Pharmaceutical Uses of Sesame Genetic Resources, Trends in New Crops and New Uses; pp 153-156, J. Janick and A. Whipkey (eds) ASHS Press; Alexandria, Va. (2002)]. Sesamin has also been known to modulate the PUFA pathways by inhibiting delta.sup.5-desaturase so that they produce less inflammatory mediators (Dachtler, M., Vande Put, F. H. M., Stijn, F: V., Beindorff, C. M and Fritsche, J., Eur. J. Lipid. Sci. Technol. 105,488-496,2003). Other benefits include lowering of serum triglycerides, reduction of high blood pressure, prevention of allergic reactions, enhancement of vitamin E activity, cancer prevention etc.
Lignans in Sesame oil is also reported to have antioxidant properties. Products of lipid oxidation are known to be health hazards since they are associated with ageing, membrane damage, heart disease and cancer (Cosgrove, J. P., Church, D. F and Pryor, W. A., Lipids, 22,299-304,1987). Lipid oxidation lowers-quality and nutritional value of foods. The addition of antioxidant is effective in retarding the oxidation of lipids and lipid containing foods. Synthetic antioxidants such as Butylated Hydroxy Anisole (BHA), Butylated Hydroxy Toluene (BHT) and Tertiary Butyl Hydroxy Quinone (TBHQ) are widely used in the food industry because they are effective and less expensive than natural antioxidant [Pin-Der, Duh and Gow-Chin, Yen., JAOCS, 74(6) 745-748,1997]. Their safety have been questioned(Chang et al, U.S. Pat. No. 5,043,100, 1991). This warrants for preparation and evaluation of natural antioxidants suitable for food and vegetable oil protection.
Antioxidant activity in Sesame cake extract have been studied in detail by various workers (Suja, K. P., John, T. A., Selvarn, N. T., Jayalekshmi, A and Arumughan, C., Food Chemistry, 84,393-400,2004; Suja, K. P., Jayaleksmi, A and Arumughan, C., Food Chemistry, 91,213-219,2005). It was found that antioxidant extract from Sesame cake at very low concentration can be substituted for synthetic antioxidants like BHT (Suja, K. P., Jayaleksmi, A and Arumughan, C., J. Agric. Fd. Chem, 52,912-915,2004, Suja, K. P., Jayaleksmi, A and Arumughan,C., J. Sci. Fd. Agric,85,1779-1783,2005).
Lignan in Sesame oil is reported to be in the range of 1 to 2% [Hemalatha, S and Ghafoorunissa, JAOCS, 81(5), 467-470, 2004]. Considering the bioactivity as cited above, Sesame lignans could be used as nutraceutical products. However an efficient process for commercial production has not been reported. The prior art on lignan extraction from Sesame oil is mostly patent related. Shinmen et al (U.S. Pat. No. 5,211,953, 1993) developed a liver function improver comprising, as an effective ingredient, a dioxabycyclo [3.3.0] octane derivative such as Sesamin and related compounds to a food or drink containing this derivative having a liver function improving action, a cholesterol level reducing action and/or a neutral fat level reducing action. An extract composed mainly of these compounds was obtained from Sesame oil by extraction with an immiscible organic solvent. The % yield of extract reported by methanolic extraction of oil was 2 to 3% based on start material. Dispersion of methanol extract in acetone, chilling, filtration and evaporation gave a compound specific extract with only 0.62% yield expressed on start material basis. They obtained a lignan content of only 32.23% in this extract based on total lignans in the oil, the start materiel. Alternatively they have tried super critical extraction of oil and also different chromatographic techniques for isolating desired lignan from the extract. However, the yield and purity of these compounds by these techniques have not been reported in this process. Namiki et al (U.S. Pat. No. 6,278;005, 2001) reported a process of producing Sesame lignans and/or Sesame flavours contained in the Sesame oil in higher purity and yield. In this process, Sesame oil was subjected to supercritical CO2 extraction and the reported percentage yield of extracts ranged from 21-24%. The lignan content in the extract was only 1.5-3.5%. A composition for inhibiting delta.sup.5-desaturase consisting of lignan compounds, prepared for biopotency studies, by extracting Sesame seed or Sesame oil using organic solvents such as acetone, methyl ethyl ketone, diethyl ketone, methanol and ethanol has been patented by Akimoto et al (U.S. Pat. No. 5,336,496, 1994). Administering to animals, the composition showed inhibitory effects, which resulted in treatment of inflammation, thrombosis or hypertension? However, the yield and purity of the composition based on lignan content is not revealed in this process. The extraction of Sesame lignans from Sesame oil by liquid extraction with organic solvent followed by saponification and precipitation of the extract at 4° C. to obtain lignans have been reported by Dachtler et al (Euro. Lipid Sci. Technol, 105,488-496,2003). However the yield of extraction was very poor. Studies on the use of Sesame oil unsaponifiable matter (USM) as a natural antioxidant revealed that the USM possesses antioxidant properties with wide food application [Mohammed, H. M. A and Awatif, I. I., Food Chemistry, 62(3),269-276,1978]. They found that a combination of a number of minor constituents such as Tocopherol, Sesamol, Squalene and antipolymerization Sterols in the USM could have a synergistic role in increasing the oxidation stability of Sesame oil.
Most of the patents filed so far are related to preparation of lignan concentrate from Sesame oil for conducting studies on biological evaluation in animal models and human. Commercial and economic feasibility have not been addressed in terms of yield and purity in these patents. The present process reported here describes a most economical method to produce lignans with high yield and purity so that commercially the process is competitive in the international market.